/dev/null for discarding output in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to discard the output of the ls command.

Linux CLI

ls > [1]

Drag options to blanks, or click blank then click option'

A/dev/null

B/dev/zero

C/dev/stdout

D/dev/random

Attempts:

3 left

💡 Hint

Common Mistakes

Using /dev/zero or /dev/random which are for input, not discarding output.

Redirecting to /dev/stdout which shows output instead of hiding it.

Redirecting output to /dev/null discards it, so nothing is shown or saved.

2fill in blank

medium

Complete the code to discard both standard output and standard error of the grep command.

Linux CLI

grep 'pattern' file.txt > [1] 2>&1

Drag options to blanks, or click blank then click option'

A/dev/null

B/dev/stdout

C/dev/random

D/dev/zero

Attempts:

3 left

💡 Hint

Common Mistakes

Redirecting only standard output but not standard error.

Using files like /dev/zero which do not discard output.

Redirecting both output and error to /dev/null hides all messages from the command.

3fill in blank

hard

Fix the error in the code to discard only the error messages of the cat command.

Linux CLI

cat missingfile.txt 2> [1]

Drag options to blanks, or click blank then click option'

A/dev/stdout

B/dev/null

C/dev/zero

D/dev/random

Attempts:

3 left

💡 Hint

Common Mistakes

Redirecting error to /dev/stdout which shows errors instead of hiding.

Using /dev/random or /dev/zero which are not for discarding output.

Redirecting standard error (2>) to /dev/null hides error messages while showing normal output.

4fill in blank

hard

Fill both blanks to discard standard output and standard error of the find command.

Linux CLI

find /path -name '*.txt' > [1] 2> [2]

Drag options to blanks, or click blank then click option'

A/dev/null

B/dev/stdout

C/dev/zero

D/dev/random

Attempts:

3 left

💡 Hint

Common Mistakes

Redirecting one stream to /dev/null and the other to a wrong file.

Using /dev/stdout which shows output instead of hiding.

Redirecting both standard output and error separately to /dev/null discards all output.

5fill in blank

hard

Fill both blanks to discard output and error of tar command and run it in background.

Linux CLI

tar -czf archive.tar.gz folder > [1] 2> [2] & disown

Drag options to blanks, or click blank then click option'

A/dev/null

B/dev/stdout

D>/dev/null

Attempts:

3 left

💡 Hint

Common Mistakes

Adding extra arguments to disown which are not needed.

Redirecting output incorrectly with extra symbols.

Redirecting both outputs to /dev/null hides all messages. The disown command detaches the job; no extra argument is needed.

Practice

1. What does redirecting output to /dev/null do in Linux?

easy

A. It displays the output on the screen

B. It saves the output to a file named /dev/null

C. It discards the output so nothing is shown or saved

D. It sends the output to the printer

Solution

1. Step 1: Understand what /dev/null is

   /dev/null is a special file that discards anything written to it.

2. Step 2: Effect of redirecting output

   Redirecting output to /dev/null means the output is thrown away and not shown or saved.

3. Final Answer:

   It discards the output so nothing is shown or saved -> Option C

4. Quick Check:

   /dev/null discards output = D [OK]

Hint: Remember: /dev/null is like a black hole for output [OK]

Common Mistakes:

• Thinking /dev/null saves output to a file
• Confusing /dev/null with a display device
• Assuming output is printed or logged

2. Which of the following commands correctly discards only the standard error output?

easy

A. command > /dev/null

B. command 2> /dev/null

C. command > /dev/null 2>&1

D. command 1> /dev/null

Solution

1. Step 1: Identify standard error redirection syntax

   Standard error is file descriptor 2, so redirecting errors uses '2>'.

2. Step 2: Match command to discard only errors

   Using 'command 2> /dev/null' discards error output only, leaving normal output visible.

3. Final Answer:

   command 2> /dev/null -> Option B

4. Quick Check:

   2> /dev/null hides errors only = A [OK]

Hint: Use '2>' to redirect errors, '>' for normal output [OK]

Common Mistakes:

• Using '>' instead of '2>' to hide errors
• Confusing '2>&1' with error-only redirection
• Redirecting both outputs when only errors needed

3. What will be the output of this command?

ls /nonexistent 2> /dev/null

medium

A. Shows no output at all

B. Shows an error message about missing directory

C. Lists files in /nonexistent directory

D. Creates the /nonexistent directory

Solution

1. Step 1: Understand the command and redirection

   ls /nonexistent tries to list a directory that does not exist, producing an error on standard error.

2. Step 2: Effect of '2> /dev/null'

   The error message is redirected to /dev/null, so it is discarded and not shown.

3. Final Answer:

   Shows no output at all -> Option A

4. Quick Check:

   Error hidden by 2> /dev/null = C [OK]

Hint: Errors go to 2>, normal output to >; here errors hidden [OK]

Common Mistakes:

• Expecting error message to appear
• Thinking directory is created
• Confusing standard output with error output

4. You want to discard both standard output and error from a command, but your script still shows errors. What is wrong with this command?

command > /dev/null 2>1

medium

A. The command will only discard standard output

B. The command does not discard any output

C. The output is redirected to the wrong file

D. The error redirection syntax is incorrect; it should be 2>&1

Solution

1. Step 1: Analyze the error redirection syntax

   The command uses '2>1' which redirects standard error to a file named '1', not to standard output.

2. Step 2: Correct syntax for redirecting error to output

   The correct syntax to redirect standard error to the same place as standard output is '2>&1'.

3. Final Answer:

   The error redirection syntax is incorrect; it should be 2>&1 -> Option D

4. Quick Check:

   Use 2>&1 to redirect errors to output [OK]

Hint: Use '2>&1' to combine error with output redirection [OK]

Common Mistakes:

• Writing '2>1' instead of '2>&1'
• Forgetting '&' in error redirection
• Assuming '2>1' redirects errors to output

5. You want to run a script that produces both output and errors, but you want to log only errors to a file and discard normal output. Which command achieves this?

hard

A. script.sh > /dev/null 2> errors.log

B. script.sh > errors.log 2> /dev/null

C. script.sh > /dev/null 2>&1

D. script.sh 2> /dev/null > errors.log

Solution

1. Step 1: Understand output and error redirection

   '>' redirects standard output, '2>' redirects standard error.

2. Step 2: Match requirement to command

   To discard normal output, redirect it to /dev/null. To save errors, redirect standard error to errors.log.

3. Final Answer:

   script.sh > /dev/null 2> errors.log -> Option A

4. Quick Check:

   Output discarded, errors logged = B [OK]

Hint: Redirect output to /dev/null, errors to file with 2> [OK]

Common Mistakes:

• Swapping output and error redirections
• Redirecting both outputs to /dev/null
• Using wrong order causing errors to be discarded